The Mortimer Letter
Spoiler warning: Plot and/or ending details follow.
The Mortimer Letter is the letter Mortimer wrote and left for Keen to see aboard Omegamatic. However, it seems that Keen forgot the letter, as he was later surprised to hear Molly saying, in the ending sequence of Keen 6 that Mortimer is still alive. The letter is written by using Standard Galactic Alphabet. Transliterated into the Latin alphabet it looks like this:
DEAR BILLY YOU FELL FOR MY ANDROID DUPLICATE PLOY IN THE MANGLING MACHINE AND NOW YOUVE FALLEN FOR IT AGAIN IM BLOWING UP THE UNIVERSE NOT THE STUPID GALAXY THIS WAS JUST A BIG DISTRACTION DODO TAG YOURE IT MORTIMER PS GANNALECH IS HOW THESE DUMB SHIKADI PRONOUNCE GRAND INTELLECT OR DIDNT YOU NOTICE THAT MISTER THREE FOURTEEN
Why Mortimer left Keen the message is unknown. Perhaps he wanted Keen to know that he is going to destroy the Universe before finally doing so, and make Keen see how intelligent his plots are. Perhaps it is another trick, or a way to get Keen go somewhere and then try to kill him there. As The Universe Is Toast was never made, Mortimer's intentions are not completely clear to fans.
The letter also shows a rather simplistic writing style, more typical of a schoolyard bully than a genius, perhaps revealling something about Mortimer's personality. Despite his alliance with the Shikadi, he seems to dislike them. The letter remains mysterious in many respects.